1. Voltage Regulators Used to regulate input voltage from a power source
Maintains power level to within set tolerance
Prevents damage to components by acting as a buffer
Two types: Linear and Switching

2. Linear Regulators
Acts like a voltage divider
Uses FET in ohmic region

3. Switching Regulator Switches on and off rapidly to alter output
Requires Control Oscillator and charge storage components

4. Types of Switching Regulators
Buck (step down) - lowers input
Boost (step up) - raises input
Buck / Boost - lowers/raises/inverts input depending on needs and controller
Charge Pump – provides multiples of input without using any inductors

5. Linear Advantages Simple Low output ripple voltage
Excellent line and load regulation    
Fast response time to load or line changes    
Low electromagnetic interference (less noise)

6. Linear Disadvantages Low efficiency
Large space requirement if heatsink is needed 
Can not increase voltage above the input

7. Switching Advantages High Efficiency
Capable of handling higher power densities    
Structures can provide output that is greater than, less than or spanning the input voltage 

8. Switching Disadvantages
Higher output ripple voltage    
Slower transient recovery time    
EMI is produced  (Very noisy)
Generally more costly

9. Linear Regulators Darlington NPN Regulator
Dropout= 2Vbe + Vsat; Typically Vdc

10. PNP LDO Regulator Dropout= Vsat; Typically <500mV.
At light loads, this falls to 10-20mV.

11. Quasi-LDO Regulator
Dropout= Vbe + Vsat.

12. Linear Regulators
Two Considerations Ground Pin Current (Ignd), Vdo (Dropout Voltage At light loads, this falls to 10-20mV.
Here, Ignd= IL/β (Pass Transistor Gain)
Darlington’s high gain allow Ignd= a few mA (typically)
Quasi-LDO, good performance (source <10mA)
LDO, Ignd= 10-20mA, which can be up to 7% of IL
All are unconditionally stable (requires no external capacitors)

13. P-FET LDO Regulator
Advantageous because the amount of PWR dissipated is Vin * Ignd, because of the Pass FET’s low “on” voltage (~.7-.8V), only a small current is required to maintain regulation.

14. Switching Regulators – Overview
Operation relies on controlled transfer of charge from input to output.
Output node charges while switch is closed and discharges while switch is open.
Requires multi-part circuitry.
Storage of the charge to be transferred.
Control of switching scheme.
Output-stage filtering

15. Switching Regulators – Pulse Rate Modulation
Constant duty cycle
Varying frequency
Noise spectrum imposed by PRM varies and is more difficult to filter out.

16. Switching Regulators – Pulse Width Modulation
Constant frequency
Varying duty cycle
Preferred – Efficient and easy to filter out noise.

17. Switching Regulator – Continuous Mode
Current through inductor never drops to zero.
Allows for highest output power for a given input voltage, switching scheme and switch current rating.
Overall performance is better.

18. Switching Regulator – Discontinuous Mode
Current through inductor drops to zero during each cycle.
Allows for smaller inductor and thus smaller overall circuit size.
Better when output current is low.

19. Dielectric isolation vs. non-isolating
Switching Topologies
Dielectric isolation vs. non-isolating
NI: Uses – small change in Vout/Vin
DI: Uses – radiation-intense environments
Ideally Power in = Power out

20. Non-Isolating forms Examples include:
Buck, Boost, Buck/Boost, Cuk, Charge Pump

21. Buck, Boost, and Buck/Boost Circuits

22. Isolated types
Examples include: Flyback converters and Forward Converters

23. Other Considerations for Switchers
MOSFETs and Diodes
Synchronous Rectification – Getting more Efficiency
Operating Frequencies

24. Ideal Inductors
Purely Inductive

25. Real Inductors
SRF
Inductive
Capacitive
Resistive

26. Frequency-Dependence for Switching Regulators
The frequency-dependent effects limit the inductor to a useful range of frequencies.
Usually the SRF (Self-Resonant Frequency) is specified by the manufacturer.
This sets a hard upper limit. The useful limit is generally lower.

27. High Frequencies are Good
As a general rule of thumb, doubling the switching frequency allows halving the inductance.
An old DC-DC converter at 30kHz might need an inductor measuring 1” in diameter.
A modern converter operating at 1MHz can deliver the same current with an inductor measuring less than .25” in diameter.
A smaller inductor will have a smaller series resistance.

28. Series Resistance Series resistance increases losses.
It can also lead to instability in boost configurations.
Duty Cycle
Duty Cycle

29. Series Resistance - Solutions
Duty Cycle
Current sensing / overcurrent protection
Duty cycle limiting

30. Cores and Saturation No External Field In an External Field
1μm
No External Field
In an External Field
Magnetic cores increase the magnetic flux density when an external field is applied, increasing energy storage capacity and inductance.
When a core is saturated, increasing the external magnetic field results in a negligible increase in flux density.

31. Cores and Saturation The onset of saturation can occur very rapidly.
At saturation, the effective inductance decreases dramatically.
This decrease can lead to instability (increasing duty cycle, decreasing inductance).
Without current or duty cycle limiting, this can result in catastrophic failure.
The manufacturer will usually specify this as the DC saturation current, the point where the inductance reaches 10% of nominal.

32. Cores and Saturation B H
Cores also exhibit losses due to internal “friction” and eddy currents.
In switchers, these losses are usually only a small percentage of the total losses, even at saturation.
However, saturation in a DC-DC supply can cause greater resistive losses due to the drop in inductance.

33. Important Parameters
Inductance: Larger inductances have lower ripple current, but are larger and can decrease stability.
Peak Current: This is obtained from the switcher’s datasheet.
DC Current: Dependent on load requirements.
SRF: Should be well above the switcher’s operating frequency.
Series Resistance: Affects the efficiency and can affect stability.

34. A Variety of Inductors

35. Applications and Sample Circuits of Some Common Packages
National Instruments LM337 Package
3-terminal adjustable regulator
Capable of supplying 1.2V to 37V with 1.5A
Offers overload protection that is only available in ICs
Can also be used as a precision current regulator
Texas Instruments TPS32xx Package
Optimal for battery powered portable applications.
Operates a 93% efficiency at 3MHz.

36. Simple LM117 Voltage Regulator Configuration
1.2V to 25V output
C1 is only needed if the device is more that 6” from the filter capacitors.
C2 is optional – it is used to improve the transient response.

37. 5V Logic Regulator with Electronic Shutdown
Uses TTL for electronic shutdown.
Clamping of adjustment terminal programs the output to 1.2V where most loads draw little current.
1.2V is the minimum output voltage.

38. 0V to 30V Regulator
The downside is that the full output current is not available for high input/output voltages.

39. Precision Current Limiter
Iout = Vref/R1
0.8 Ohms < R1 < 120 Ohms

40. AC Voltage Regulator
Regulates a 24Vp-p Input to 12Vp-p at 1A.

41. 12V Battery Charger
Rs is used to set the output impedance of the charger:

42. Texas Instruments TPS62300 Used in low-power portable electronics
Designed for fast start-up time

43. References
TI. Understanding Buck Power Stages in Switchmode Power Supplies.
TI. Understanding Boost Power Stages in Switchmode Power Supplies.
Erickson, R. DC-DC Power Converters.
Shen, L., Kong, J. Applied Electromagnetism, Third Edition.